1. Field of the Invention
The present invention relates to a video display apparatus and a video display method displaying an image by a bidirectional scanning system.
2. Description of the Prior Art
In a conventional video display apparatus such as a television receiver or a display monitor, a unidirectional scanning system is generally employed.
FIG. 23 illustrates a conventional unidirectional progressive scanning system (sequential scanning system). In the unidirectional progressive scanning system, scanning is performed on a screen slightly obliquely downward from left to right, as shown in FIG. 23. In the progressive scanning system with 525 scanning lines, the horizontal scanning frequency is 31.5 KHz and the horizontal scanning period is 31.75 xcexcm. The frame frequency is 30 Hz, and the vertical scanning frequency is 30 Hz.
FIG. 24 illustrates a conventional unidirectional interlaced scanning system. In the unidirectional interlaced scanning system, odd numbered scanning lines are scanned in first fields as shown by solid lines, and even numbered scanning lines are scanned in second fields as shown by one-dot chain lines in FIG. 24. A single complete image is displayed by scanning of one frame consisting of a first field and a second field. In the interlaced scanning system with 525 scanning lines, the horizontal scanning frequency is 31.5 KHz and the horizontal scanning period is 31.75 xcexcs. The frame frequency is 30 Hz, the field frequency is 60 Hz, and the vertical scanning frequency is 60 Hz.
A bidirectional scanning system is recently proposed for attaining higher picture quality. FIG. 25 illustrates a bidirectional progressive scanning system. As shown in FIG. 25, odd numbered scanning lines are horizontally scanned from left to right on a screen, and even numbered scanning lines are scanned from right to left on the screen.
In the bidirectional scanning system, the density of the scanning lines is doubled in the vertical direction, to increase the resolution and improve the brightness. Further, power for deflecting an electron beam is reduced due to reciprocating deflection, and a power circuit can be reduced in scale.
However, a generally employed video signal is processed in accordance with the unidirectional progressive scanning system or the unidirectional interlaced scanning system, and hence a conventional video display apparatus cannot directly display an input video signal in the bidirectional scanning system.
In this regard, awaited are a video display apparatus and a video display method capable of displaying a video signal of the unidirectional progressive scanning system or the unidirectional interlaced scanning system in the bidirectional scanning system.
When converting such a video signal of the unidirectional scanning system to that of the bidirectional scanning system, a conversion method responsive to the type of the original video signal must be applied in order to improve the picture quality.
An object of the present invention is to provide a video display apparatus and a video display method capable of displaying a video signal of a unidirectional progressive scanning system or a unidirectional interlaced scanning system as an image of high picture quality in a bidirectional scanning system.
A video display apparatus according to an aspect of the present invention comprises a conversion circuit, a scanning line reversion circuit and a display part. The conversion part receives a first video signal of an interlaced scanning system or a progressive scanning system including a first number of scanning lines in each frame and having a first vertical scanning frequency, and converts the first video signal to a second video signal of a progressive scanning system including a second number of scanning lines in each frame and having a second vertical scanning frequency. The scanning line reversion circuit alternately reverses the time base of the second video signal output from the conversion circuit every scanning line and outputs the processed second video signal as a third video signal. The display part displays the third video signal output from the scanning line reversion circuit by bidirectional scanning in synchronization with a vertical synchronizing signal and a horizontal synchronizing signal after conversion by the conversion circuit.
In the video display apparatus, the first video signal of an interlaced scanning system or a progressive scanning system including the first number of scanning lines in each frame and having the first vertical scanning frequency is converted to the second video signal of a progressive scanning system including the second number of scanning lines in each frame and having the second vertical scanning frequency. The time base of the second video signal is alternately reversed every scanning line, and the processed second video signal is output as the third video signal. Further, the third video signal is displayed by bidirectional scanning in synchronization with the vertical synchronizing signal and the horizontal synchronizing signal after conversion by the conversion circuit. Thus, a video signal of a unidirectional interlaced scanning system or a unidirectional progressive scanning system is displayed as an image of high picture quality in a bidirectional scanning system.
The first number may be an odd number. In this case, a video signal of an interlaced scanning system or a progressive scanning system including the odd number of scanning lines in each frame and having the first vertical scanning frequency is displayed by bidirectional scanning with the second number of scanning lines and the second vertical scanning frequency.
The first number may be an even number. In this case, a video signal of an interlaced scanning system or a progressive scanning system including an even number of scanning lines in each frame and having the first vertical scanning frequency is displayed by bidirectional scanning with the second number of scanning lines and the second vertical scanning frequency.
The video display apparatus may further comprise a first offset circuit displacing the vertical synchronizing signal by a first offset time every frame.
In this case, the scanning direction for each scanning line can be alternately reversed every frame by setting the first offset time at a prescribed value. Thus, even if an error occurs between the forward scanning time and the backward scanning time or between the brightness of forward scanning lines and that of backward scanning lines, such an error is averaged on the time base to cause no deterioration of the picture quality. Thus, design accuracy for the display part is relaxed.
The first offset time may be half a horizontal scanning period. In this case, the scanning direction for each scanning line is alternately reversed every frame.
The second vertical scanning frequency may be equal to the first vertical scanning frequency. In this case, a video signal of an interlaced scanning system or a progressive scanning system including the first number of scanning lines in each frame and having the first vertical scanning frequency is displayed by bidirectional scanning with the second number of scanning lines and the same vertical scanning frequency as the first vertical scanning frequency.
The second vertical scanning frequency may be even times the first vertical scanning frequency. In this case, a video signal of an interlaced scanning system or a progressive scanning system including the first number of scanning lines in each frame and having the first vertical scanning frequency is displayed by bidirectional scanning with the second number of scanning lines and a vertical scanning frequency even times the first vertical scanning frequency.
The video display apparatus may further comprise a second offset circuit displacing the vertical synchronizing signal so that a plurality of fields included in each frame keep interlaced relation.
In this case, the vertical synchronizing signal is so displaced that the plurality of fields included in each frame can keep interlaced relation. Thus, the picture quality can be improved.
The second vertical scanning frequency may be twice the first vertical scanning frequency, and the second offset circuit may displace the vertical synchronizing signal by a second offset time every other field of each frame.
In this case, a video signal of an interlaced scanning system or a progressive scanning system including the first number of scanning lines in each frame and having the first vertical scanning frequency is displayed by bidirectional scanning with the second number of scanning lines and the vertical scanning frequency twice the first vertical scanning frequency, while odd and even fields of each frame can keep interlaced relation. Thus, the picture quality can be improved.
The second offset time may be xc2xc the horizontal scanning period. Thus, odd and even fields of each frame can keep interlaced relation.
The second number may be even times the first number. In this case, a video signal of an interlaced scanning system or a progressive scanning system is displayed by bidirectional scanning with scanning lines of even times. Thus, the picture quality can be improved.
The second number may be equal to the first number. In this case, a video signal of an interlaced scanning system or a progressive scanning system is displayed by bidirectional scanning with the same number of scanning lines.
The first video signal may be of an interlaced scanning system, the first number may be an odd number, the first vertical scanning frequency may be even times the second vertical scanning frequency, each frame may include a plurality of fields, and the vertical synchronizing signal may be displaced so that the plurality of fields of each frame keep interlaced relation.
In this case, a video signal of an interlaced scanning system including an odd number of scanning lines in each frame and having the first vertical scanning frequency is displayed by bidirectional scanning with the second number of scanning lines and a vertical scanning frequency even times the first vertical scanning frequency, while the plurality of fields of each frame can keep interlaced relation. Thus, a high picture quality is attained.
A video display method according to another aspect of the present invention includes steps of receiving a first video signal of an interlaced scanning system or a progressive scanning system including a first number of scanning lines in each frame and having a first vertical scanning frequency and converting the first video signal to a second video signal of a progressive scanning system including a second number of scanning lines in each frame and having a second vertical scanning frequency, alternately reversing the time base of the second video signal every scanning line and outputting the processed second video signal as a third video signal, and displaying the third video signal by bidirectional scanning in synchronization with a vertical synchronizing signal and a horizontal synchronizing signal after conversion.
In the video display method, the first video signal of an interlaced scanning system or a progressive scanning system including the first number of scanning lines in each frame and having the first vertical scanning frequency is converted to the second video signal of a progressive scanning system including the second number of scanning lines in each frame and having the second vertical scanning frequency. The time base of the second video signal is alternately reversed every scanning line, and the processed second video signal is output as the third video signal. Further, the third video signal is displayed by bidirectional scanning in synchronization with the vertical synchronizing signal and the horizontal synchronizing signal after conversion. Thus, a video signal of a unidirectional interlaced scanning system or a unidirectional progressive scanning system is displayed in a bidirectional scanning system as an image of high picture quality.
The first number may be an odd number. In this case, a video signal of an interlaced scanning system or a progressive scanning system including an odd number of scanning lines in each frame and having the first vertical scanning frequency is displayed by bidirectional scanning with the second number of scanning lines and the second vertical scanning frequency.
The first number may be an even number. In this case, a video signal of an interlaced scanning system or a progressive scanning system including an even number of scanning lines in each frame and having the first vertical scanning frequency is displayed by bidirectional scanning with the second number of scanning lines and the second vertical scanning frequency.
The video display method may further include a step of displacing the vertical synchronizing signal by a first offset time every frame.
In this case, the scanning direction for each scanning line can be alternately reversed every frame by setting the first offset time at a prescribed value. Thus, even if an error occurs between the forward scanning time and the backward scanning time or between the brightness of forward scanning lines and that of backward scanning lines, such an error is averaged on the time base to cause no deterioration of the picture quality. Thus, design accuracy for a display part is relaxed.
The first offset time may be half a horizontal scanning period. In this case, the scanning direction for each scanning line is alternately reversed every frame.
The second vertical scanning frequency may be equal to the first vertical scanning frequency. In this case, a video signal of an interlaced scanning system or a progressive scanning system including the first number of scanning lines in each frame and having the first vertical scanning frequency is displayed by bidirectional scanning with the second number of scanning lines and the same vertical scanning frequency as the first vertical scanning frequency.
The second vertical scanning frequency may be even times the first vertical scanning frequency. In this case, a video signal of an interlaced scanning system or a progressive scanning system including the first number of scanning lines in each frame and having the first vertical scanning frequency is displayed by bidirectional scanning with the second number of scanning lines and a vertical scanning frequency even times the first vertical scanning frequency.
The video display method may further include a step of displacing the vertical synchronizing signal so that a plurality of fields included in each frame keep interlaced relation.
In this case, the vertical synchronizing signal is so displaced that the plurality of fields included in each frame can keep interlaced relation. Thus, the picture quality can be improved.
The second vertical scanning frequency may be twice the first vertical scanning frequency, and the step of displacing the vertical synchronizing signal may include a step of displacing the vertical synchronizing signal by a second offset time every other field of each frame.
In this case, a video signal of an interlaced scanning system or a progressive scanning system including the first number of scanning lines in each frame and having the first vertical scanning frequency is displayed by bidirectional scanning with the second number of scanning lines and the vertical scanning frequency twice the first vertical scanning frequency, while odd and even fields of each frame can keep interlaced relation. Thus, the picture quality can be improved.
The second offset time may be xc2xc a horizontal scanning period. Thus, odd and even fields of each frame can keep interlaced relation.
The second number may be even times the first number. In this case, a video signal of an interlaced scanning system or a progressive scanning system is displayed by bidirectional scanning with scanning lines of even times. Thus, the picture quality can be improved.
The second number may be equal to the first number. In this case, a video signal of an interlaced scanning system or a progressive scanning system is displayed by bidirectional scanning with the same number of scanning lines.
The first video signal may be of an interlaced scanning system, the first number may be an odd number, the first vertical scanning frequency may be even times the second vertical scanning frequency, each frame may include a plurality of fields, and the video display method may further include a step of displacing the vertical synchronizing signal so that the plurality of fields of each frame keep interlaced relation.
In this case, a video signal of an interlaced scanning system including an odd number of scanning lines in each frame and having the first vertical scanning frequency is displayed by bidirectional scanning with the second number of scanning lines and a vertical scanning frequency even times the first vertical scanning frequency, while the plurality of fields of each frame can keep interlaced relation. Thus, a high picture quality is attained.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.